Hopefully someone can help me figure this out. I've got an 06 F350 6.0l and about 2 weeks ago while driving uphill at around 65mph, there was a sudden hissing sound and it sounded like a tire got punctured. It wasn't my tire. Every time I'm building boost, it makes a hissing sound like an air leak and I can hear it from around the bottom of the steering wheel at the firewall area. I've checked the cac tubes and the exhaust flex joints and don't see any black soot. I can't just let it idle and try to find the leak since it only happens under boost. FYI - there are no MIL codes. I appreciate any help I can get. Thank you.